In a wireless communication system, the notions of sleep state and paging are important to provide network connectivity to a large population of wireless devices, e.g., wireless terminals, in a battery power efficient and air link resource efficient manner. Wireless terminals may be implemented as various mobile devices.
Sleep state provides a wireless terminal with a mode of operation to minimize battery power consumption by shutting down the whole or part of the terminals transmit/receive circuitry. In addition, in some systems, a wireless terminal in the sleep state is not allocated any dedicated air link resource and therefore a large number of users can be simultaneously supported. During time intervals where the wireless terminal has no traffic activity, the wireless terminal can stay in the sleep state thus conserving resources.
Paging involves waking up the wireless terminal periodically from the sleep state and operating the wireless terminal to receive and process paging messages (if transmitted) in a downlink, e.g., in communications from a base station to the wireless terminal. The base station usually knows when the wireless terminal should wake up. Thus, if the base station intends to contact, or page, the wireless terminal, the base station can send a paging message in a downlink paging (DLPG) channel at the time when the wireless terminal will wake up and monitor the channel. If the wireless terminal does not receive any message for it in the DLPG channel, the wireless terminal can go back to the sleep state. Otherwise, the wireless terminal should carry out any operations specified in the paging message. For example, a wireless terminal may just receive the messages and go back to the sleep state. Alternatively, the wireless terminal may access the base station to establish active connection with the base station.
The time interval between two successive wake-up periods is called a paging cycle. It is during the portion of the paging cycle when a wireless terminal is not doing processing related to receiving a page that a wireless terminal can operate in a sleep state. In order to maximize the benefit of the sleep state, known paging systems generally use a large value for the paging cycle. For example, in a voice system, e.g., IS-95, the typical paging cycle is about 1 to 3 seconds. In data systems, the paging cycle can be even larger. For example, in 1xEV DO, the typical paging cycle is about 5 seconds. In known systems, when the wireless terminal wakes up, in order to receive the DLPG channel, the wireless terminal usually needs to carry out certain physical layer operations, such as synchronizing the receiver with the downlink signal and training the channel estimation for the downlink channel. In addition, the DLPG channel transmission generally occupies a relatively long time period and typically contains short instructional messages as well as identification information. For example, a paging message transmission in the IS-95 system may occupy 80 milli-seconds. Hence, when the wireless terminal wakes up, it generally consumes quite amount of battery power to complete all the required operations with the device operating for, e.g., 80 milli-seconds or more at full power during each period in which a page may be received. This known paging method is well suited for establishing end-to-end set-up for conventional communications services such as voice channels which may have a relatively long duration and can support a fair amount of delay, e.g., several seconds, between paging periods.
However, a large paging cycle (which conserves power) results in a large paging latency, which is not suitable for various emerging services, such as push-to-talk. These emerging services may require a very small paging latency, e.g., cycles well under a second, to give a user a sense of an immediate response. For example, in a push-to-talk system, to minimize the call set-up time, the desired paging cycle may be about 100 milli-seconds, which is much shorter than what many known paging system can support. Note that the with known paging systems such as that used in IS-95 it is unlikely that these systems will be able to simply reduce the paging cycle dramatically to meet such a requirement. This is because of the large amount of battery power consumption required in each wake-up period in the known paging systems due, in part, to the channel estimation process. In such systems if a small paging cycle were used, the amount of power consumed due to the frequent wake-up operations would result in a user having to recharge the device's battery very frequently, which is unpractical. Therefore, there is a need for an efficient paging system that can meet the low paging latency requirements of these new emerging services. It would be highly desirable if low paging latency could be achieved without significantly increasing the overall battery power consumption rate as compared to existing devices.
Based upon the above discussion, it is clear that improved methods of paging are needed which increase the paging efficiency of the wireless communications system in order to meet the low paging latency requirements of new emerging services, such as push-to-talk and/or to reduce the rate of battery power consumption with existing services. New paging methods that reduce battery power consumption of wireless terminals facilitate opportunities for repeat pages of failed paging attempts, and/or limit system interference due to paging signaling would be beneficial. Paging improvements developed to meet the requirements of new emerging services could also be beneficially used in existing conventional services system applications to increase overall efficiency and conserve resources and need not be limited to applications which require or use low latency paging.